Process for preparing a polyimide and a composite material containing the same

ABSTRACT

This invention relates to a method for preparing a polyimide having good heat-stability and excellent flowability in a molten state. 
     The polymide is prepared by reacting aromatic diamines such as 4,4&#39;-bis(3-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl] ketone and bis [4-(3-aminophenoxy)phenyl] sulfone; tetracarboxylic dianhydrides such as pyromellitic dianhydride, 3,3&#39;, 4,4&#39;-benzophenonetetracarboxylic dianhydride and bis(3,4-dicarboxyphenyl) ether dianhydride; and dicarboxylic anhydrides such as glutaric anhydride, 1,2-hexanedicarboxylic anhydride, phthalic anhydride and 3,4-benzophenonedicarboxylic anhydride. The molar ratio of aromatic diamine: tetracarboxylic dianhydride: dicarboxylic anhydride is 1:(0.9 to 1.0):(0.001 to 1.0). 
     The invention also relates to polyimide composite materials which are excellent in mechanical strengths and processability. The materials contain the polyimide and fibrous reinforcing materials such as yarn, roving, tow, fabrics, mats and felts of glass fiber, carbon fibers or aromatic polyamide fibers.

BACKGROUND OF THE INVENTION

The present invention relates to a process for preparing a polyimide forfusion molding that has excellent thermal stability and processabilityin a molten state.

The present invention also relates to a polyimide composite materialthat has excellent high-temperature stability, chemical resistance andmechanical strength as well as outstanding processability.

A polyimide obtained by reacting tetracarboxylic dianhydride andaromatic diamine has excellent mechanical strength, dimensionalstability, high temperature stability flame resistance and electricalinsulation properties. Such a polyimide has been used in electrical andelectronic appliances, space and aeronautical instruments and transportmachinery. It is expected that it will also be used in applicationswhere high-temperature resistance is required.

A variety of polyimides exhibiting excellent properties have beendeveloped. Some polyimides, however, have no distinct glass transitiontemperature, although they are excellent in high-temperature stability.As a result, when employed as molding materials, specific methods suchas sinter molding must be used for processing. Other polyimides whichare excellent in processability have low glass transition temperaturesand are soluble in haloganated hydrocarbons, which renders thesepolyimides unsatisfactory for use in applications which require ahigh-temperature stability and solvent resistance. Thus, thesepolyimides have numerous advantages and disadvantages.

The present inventors have previously discovered a polyimide that isexcellent in mechanical strength, thermal characteristics, electricalproperties and solvent resistance and exhibits high-temperaturestability. The polyimide consists primarily of recurring units of theformula: ##STR1## wherein X represents a direct bond or a radicalselected from the group consisting of a C₁ -C₁₀ divalent hydrocarbonradical, a hexafluorinated isopropylidene radical, a carbonyl radical, athio radical and a sulfonyl radical; Y₁, Y₂, Y₃ and Y₄ represent aradical selected from the group consisting of a hydrogen atom, a loweralkyl radical, a lower alkoxy radical, a chlorine atom and a bromineatom; and R represents a tetravalent radical selected from the groupconsisting of an aliphatic radical having 2 or more carbon atoms, acyclic aliphatic radical, a monocyclic aromatic radical, a fusedpolycyclic aromatic radical, and a polycyclic aromatic radical whereinthe aromatic rings are linked together directly or via a bridged member.The polyimides have been disclosed in the following Japanese Laid-OpenPatents.

Ohta et al.; TOKKAISHO 61-143478 (1986)

Tamai et al.; TOKKAISHO 62-68817 (1987) which corresponds to copendingUnited States patent application Ser. No. 44,028, filed on June 30, 1986now U.S. Pat. No. 4,897,349

Ohta et al.; TOKKAISHO 62-86021 (1987) which corresponds to copendingUnited States patent application Ser. No. 44,028, filed on June 30, 1986now U.S. Pat. No. 4,897,349

Ohta et al.; TOKKAISHO 62-235381 (1987) and

Oikawa et al.; TOKKAISHO 63-128025 (1988) which corresponds to copendingUnited States patent application Ser. No. 119,042, filed on Nov. 10,1987 now U.S. Pat. No. 4,908,409

The polyimide is a novel high-temperature stable resin having many goodproperties.

The polyimide exhibits excellent flowability and good processability.The fused resin, however, gradually exhibits decreased flowability whichhas an adverse effect on the processability when the polyimide is keptat high temperatures for a long period of time, for example, longresidence at high temperatures in a cylinder in the injection molding.

Therefore, it is desirable to develop a polyimide which exhibits goodflowability at lower temperatures and stable flowability for a longperiod of time during processing.

Previously produced molded products prepared by using compositematerials composed of polyimides and fibrous reinforcing materialsexhibit excellent mechanical strengths, particularly strength retentionat high temperatures and are also outstanding in solvent resistance anddimensional stability. Such molded products are desirable for use asstructural members for space crafts and the like.

Polyimides, generally have a high melt viscosity. Therefore compositematerials containing these polyimides as matrices have required severeprocessing conditions as compared to those containing matrices ofengineering plastics such as polycarbonate and polyethyleneterephathalate, thereby causing various problems.

Special polyimides having low melt viscosity and excellent workabilityhave also been known in the art. Such polyimides, however, have a lowheat distortion temperature and are soluble in solvents such ashaloganated hydrocarbons. Consequently, the composites containing such aresin as a matrix have caused problems in high-temperature stability andchemical resistance.

In order to overcome these problems, a composite material containing apolyimide having above stated good properties and fibrous reinforcingmaterials has been developed [Koba et al.; Japanese Laid-Open PatentTOKKAISHO 62-248635 (1987)]. The polyimide, however, gradually decreasesits melt flowability when maintained at high temperatures for a longperiod. This phenomenon often inhibits continuous operation.Accordingly, the development of polyimide composite materials which arecapable of operating for a long period of time and also provideexcellent properties is strongly desired.

SUMMARY OF THE INVENTION

An object of this invention is to provide a method for preparing anexcellent polyimide which has, in addition to its substantiallyoutstanding properties, good thermal stability in a molten state anddoes not deteriorate processability even after residence in hightemperatures for a long period of time.

Another object of this invention is to provide a polyimide basecomposite material capable of being stably processed for a long periodof time without giving adverse effect on the essential properties of thepolyimide such as high-temperature stability, chemical resistance anddimensional stability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 and FIG. 5 illustrate the relationship between share rate andmelt viscosity of the polyimide prepared by the process of thisinvention.

FIG. 2 and FIG. 6 illustrate the relationship between the melt viscosityand numbers of repeated fusion.

FIG. 3 and FIG. 4 illustrate the relationship between the melt viscosityand residence time of the polyimide in the cylinder of flow tester inthis invention.

FIG. 7 shows an example of equipment for preparing the polyimide basecomposite material.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for preparing a thermallystable polyimide consisting primarily of recurring units of the formula:##STR2## wherein X represents a direct bond or a radical selected fromthe group consisting of a C₁ -C₁₀ divalent hydrocarbon radical, ahexafluorinated isopropylidene radical, a carbonyl radical, a thioradical and a sulfonyl radical; Y₁, Y₂, Y₃ and Y₄ may be the same ordifferent and represent a radical selected from the group consisting ofa hydrogen atom, a lower alkyl radical, a lower alkoxy radical, achlorine atom and bromine atom; and R represents a tetravalent radicalselected from the group consisting of an aliphatic radical having 2 ormore carbon atoms, a cyclic aliphatic radical, a monocyclic aromaticradical, a fused polycyclic aromatic radical, and a polycyclic aromaticradical wherein the aromatic rings are linked together directly or via abridged member.

The process of the present invention comprises reacting

(a) an aromatic diamine represented by the formula (I) ##STR3## whereinX, Y₁, Y₂, Y₃ and Y₄ have the same meanings as set forth above.

(b) a tetracarboxylic dianhydride represented by the formula (II)##STR4## wherein R is as above defined, (c) a dicarboxylic anhydriderepresented by the formula (III) ##STR5## wherein Z represents adivalent radical selected from the group consisting of an aliphaticradical, a cyclic aliphatic radical, a monocyclic aromatic radical, afused polycyclic aromatic radical, and a polycyclic aromatic radicalwherein the aromatic radicals are linked to one another directly or viabridged member, form a polyamic acid, and dehydrating or imidizing thepolyamic acid to form a polyimide. Preferably, the molar ratio of thetetracarboxylic dianhydride is from about 0.9 to about 1.0 mole per moleof aromatic diamine and, preferably the molar ratio of the dicarboxylicanhydride is from about 0.001 to about 1.0 mole per mole of diamine.

Exemplary suitable aromatic diamines for use in the process of thisinvention includes, bis[4-(3-aminophenoxy)phenyl]methane,1,1-bis[4-(3-aminophenoxy)phenyl]ethane,2,2-bis[4-(3-aminophenoxy)phenyl]propane,

2-[4-(3-aminophenoxy)phenyl]-2-[4-(3-aminophenoxy)-3-methylphenyl]-propane,2,2-bis[4-(3-aminophenoxy)-3-methylphenyl]propane,

2-[4-(3-aminophenoxy)phenyl]-2-[4-(3-aminophenoxy)-3,5dimethylphenyl]propane,

2,2-bis[4-(3-aminophenoxy)-3,5-dimethylphenyl]propane,

2,2-bis[4-(3-aminophenoxy)phenyl]butane,

2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane,

4,4'-bis(3-aminophenoxy)biphenyl,

4,4'-bis(3-aminophenoxy)-3-methylbiphenyl,

4,4'-bis(3-aminophenoxy)-3,3'-dimethylbiphenyl,

4,4'-bis(3-aminophenoxy)-3,5-dimethylbiphenyl,

4,4'-bis(3-aminophenoxy)-3,3',5,5'-tetramethylbiphenyl,

4,4'-bis(3-aminophenoxy)-3,3'-dichlorobiphenyl,

4,4'-bis(3-aminophenoxy)-3,5-dichlorobiphenyl,

4,4'-bis(3-aminophenoxy)-3,3',5,5'-tetrachlorobiphenyl,

4,4'-bis(3-aminophenoxy)-3,3'-dibromobiphenyl,

4,4'-bis(3-aminophenoxy)-3,5-dibromobiphenyl,

4,4-bis(3-aminophenoxy)-3,4',5,5'tetrabromobiphenyl,

bis[4-(3-aminophenoxy)phenyl]ketone,bis[4-(3-aminophenoxy)phenyl]sulfide,bis[4-(3-aminophenoxy)-3-methoxyphenyl]sulfide,

[4-(3-aminophenoxy)phenyl][4-(3-aminophenoxy)-3,5-dimethyoxyphenyl]sulfide,bis[4-(3-aminophenoxy)-3,5-dimethoxyphenyl]sulfide, andbis[4-3-aminophenoxy)phenyl] sulfone.

Preferably aromatic diamines selected from the group consisting of

4,4'-bis(3-aminophenoxy)biphenyl,

2,2-bis[4-(3-aminophenoxy)phenyl]propane,

bis[4-(3-aminophenoxy)phenyl]ketone, bis(4-(3-aminophenoxy)phenyl]sulfide and bis[4-(3-aminophenoxy)phenyl]sulfone are employed. Thediamine compound may be used singly or in combination.

Other diamines may be used in the process of the invention so long asadverse effect on the properties of the polyimide produced by theprocess of this invention.

Exemplary suitable tetracarboxylic dianhydrides for use in the processof this invention include ethylenetetracarboxylic dianhydride,butanetetracarboxylic dianhydride, cyclopentanetetracarboxylicdianhydride, pyromellitic dianhydride,

1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride,

bis(2,3-dicarboxyphenyl)methane dianhydride,

bis(3,4-dicarboxypenyl)methane dianhydride,

2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,

2,2-bis(2,3-dicarboxyphenyl)propane dianhydride,

2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride,

2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride,3,3',4,4'-benzophenonetetracarboxylic dianhydride,

2,2',3,3'-benzophenonetetracarboxylic dianhydride,

3,3',4,4'-biphenyltetracarboxylic dianhydride,

2,2',3,3'-biphenyltetracarboxylic dianhydride,

bis(3,4-dicarboxyphenyl) ether dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl) sulfone dianhydride,

4,4'-(p-phenylenedioxy)diphthalic dianhydride,

4,4'-(m-phenylenedioxy)diphthalic dianhydride,

2,3,6,7-naphthalenetetracarboxylic dianhydride,

1,4,5,8-naphthalenetetracarboxylic dianhydride,

1,2,5,6-naphthalenetetracarboxylic dianhydride,

1,2,3,4-benzenetetracarboxylic dianhydride,

3,4,9,10-perylenetetracarboxylic dianhydride,

2,3,6,7-anthracenetetracarboxylic dianhydride and

1,2,7,8-phenanthrenetetracarboxylic dianhydride.

Preferred tetracarboxylic dianhydrides for use in the process of thisinvention include pyromellitic dianhydride,3,3'4,4'-benzophenonetetracarboxylic dianhydride,3,3',4,4'-biphenyltetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride and

4,4'-(p-phenylenedioxy)diphthalic dianhydride. The tetracarboxylicdianhydride may be used singly or in combination of two or more

Dicarboxylic anhydride used in the method of this invention includes,for example, malonic anhydride, succinic anhydride, glutaric anhydride,adipic anhydride, pimelic anhydride, suberic anhydride, azelaicanhydride, sebacic anhydride, methylmalonic anhydride, ethylmalonicanhydride, dimethylmalonic anhydride, methylsuccinic anhydride,2,2-dimethylsuccinic anhydride, 2,3-dimethylsuccinic anhydride,tetramethylsuccinic anhydride, maleic anhydride, citraconic anhydride,glutaconic anhydride, methylenesuccinic anhydride, allylmalonicanhydride, tellaconic anhydride, muconic anhydride,1,2-cyclobutanedicarboxylic anhydride, 1,2-cyclohexanedicarboxylicanhydride, cyclohexenedicarboxylic anhydride, camphoric anhydride,phthalic anhydride, 2,3-benzophenonedicarboxylic anhydride,3,4-benzophenonedicarboxylic anhydride, 2,3-dicarboxyphenyl phenyl etheranhydride, 3,4-dicarboxyphenyl phenyl ether anydride,2,3-biphenyldicarboxylic anhydride, 3,4-biphenyldicarboxylic anhydride,2,3-dicarboxyphenyl phenyl sulfone anhydride, 3,4-dicarboxyphenyl phenylsulfone anhydride, 2,3-dicarboxyphenyl phenyl sulfide anhydride,3,4-dicarboxyphenyl phenyl sulfide anhydride,1,2-naphthalenedicarboxylic anhydride, 2,3-naphthalenedicarboxylicanhydride, 1,8-naphthalenedicarboxylic anhydride,1,2-anthracenedicarboxylic anhydride, 2,3-anthracenedicarboxylicanhydride and 1,9-anthracenedicarboxylic anhydride.

Preferred anhydrides for use in the process of this invention includeglutaric anhydride, citraconic anhydride, tetraconic anhydride,1,2-cyclobutanedicarboxylic anhydride, 1,2-hexanedicarboxylic anhydride,phthalic anhydride, 3,4-benzophenonedicarboxylic anhydride,3,4-dicarboxyphenyl phenyl ether anhydride, 3,4-biphenyldicarboxylicanhydride, 3,4-dicarboxyphenyl phenyl sulfide anhydride and3,4-dicarboxyphenyl phenyl sulfone. The above mentioned dicarboxylicanhydride may be used singly or in combination of the two or more.

Preferably, the molar ratio of the aromatic diamine, tetracarboxylicdianhydride and dicarboxylic anhydride are from about 0.9 to about 1.0mole of tetracarboxylic dianhydride and from about 0.001 to about 1.0mole of dicarboxylic anhydride per mole of aromatic diamine.

In preparing the polyimide, the molar ratio of the aromatic diamine tothe tetracarboxylic dianhydride is usually adjusted to control themolecular weight of the polyimide formed. In the method of thisinvention, when the molar ratio of the tetracarboxylic dianhydride tothe aromatic diamine is in the range of from about 0.9 to about 1.0 apolyimide having good melt viscosity is obtained.

The amount of dicarboxylic anhydride simultaneously present in thereaction is preferably in the range of from about 0.001 to about 1.0mole per mole of aromatic diamine. When the amount is less than 0.001mole, heat stability in the molten state of polyimide which is theobject of this invention may not be obtained. When the molar ratio ofthe dicarboxylic anhydride to the aromatic diamine is greater than 1.0the mechanical properties of molded products are not as good. Mostpreferably, the molar ratio of the dicarboxylic anhydride to thearomatic diamine is from about 0.01 to about 0.05 mole of dicarboxylicanhydride per mole of aromatic diamine.

Suitable organic solvents for use in the method of this inventioninclude.

N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide,

N,N-dimethylmethoxyacetamide, N-methyl-2-pyrolidone,

1,3-dimethyl-2-imidazolidinone, N-methylcaprolactam,

1,2-dimethoxyethane, bis(2-methoxyethyl) ether,

1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether,tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, pyridine, picoline, dimethylsulfoxide, dimethyl sulfone, tetramethylurea, hexamethylphosphoramide,phenol, m-cresol, p-cresol, p-chlorophenol and anisole. The organicsolvents may be used singly or in combination.

In the method of this invention, the starting materials, e.g. thearomatic diamine, tetracarboxylic dianhydride and dicarboxylic anhydrideare added to the organic solvent and reacted. The reaction can becarried out by any of the following methods.

(a) After reacting aromatic diamine with tetracarboxylic dianhydride,dicarboxylic anhydride is added and reacted.

(b) After reacting aromatic diamine with dicarboxylic anhydride,tetracarboxylic dianhydride is added and reacted.

(c) Aromatic diamine, tetracarboxylic dianhydride and dicarboxylicanhydride are reacted at the same time.

The reaction temperature is preferably in the range of from about 0° toabout 250° C. and preferably 60° C. or less.

Any reaction pressure may be used and ambient pressure is enough tocarry out the reaction.

The reaction time is dependent upon the aromatic diamine,tetracarboxylic dianhydride, dicarboxylic anhydride, solvent andreaction temperature. Preferably, the reaction time is from about 4 toabout 24.

Polyamic acid is formed by the above mentioned reaction. The resultantpolyamic acid is dehydrated by heating at 100° to 400° C. or chemicallyimidized by using a usual imidizing agent such as acetic anhydride. Thepolyimide obtained consists primarily of recurring units of the formula:##STR6## wherein X, Y₁, Y₂, Y₃ Y₄ and R are as above defined.

The polyamic acid is generally formed at low temperatures and thenthermally or chemically imidized. The polyimide, however, can also beobtained by simultaneously conducting the formation and thermalimidization of the polyamic acid at a temperature of from about 60° toabout 250° C. In this method, an aromatic diamine, tetracarboxylicdianhydride and dicarboxylic anhydride are suspended or dissolved in anorganic solvent and reacted by heating. Thus formation and imidizationof the polyamic acid are carried out at the same time and produce apolyimide consisting primarily of the recurring units of the aboveformula.

When the polyimide of this invention is processed by fusion molding,other thermoplastic resins may be incorporated in a suitable amountdepending upon the application so long as no adverse effects occurcontrary to the objects of this invention. Illustrative examples ofthermoplastic resins suitable for use with the polyimide includepolyethylene, polypropylene, polycarbonate, polyarylate, polyamide,polysulfone, polyethersulfone, polyetherketone, polyphenylenesulfide,polyamideimide, polyetherimide and modified polyphenyleneoxide.

Fillers which are used for usual resin compositions may be employed inamounts which have no adverse effects on the objects of this invention.Suitable fillers include wear resistance improvers such as graphite,carborundum, quartz powder, molybdenum disulfide and fluororesins;reinforcing materials such as glass fiber, carbon fiber, boron fiber,silicon carbide fiber, carbon whisker, asbestos, metal fiber and ceramicfiber; flame retardants such as antimony trioxide, magnesium carbonateand calcium carbonate; electrical property improvers such as clay andmica; tracking resistance improvers such as barium sulfate, silica andcalcium metasilicate; thermal conductivity improvers such as ironpowder, zinc powder, aluminum powder and copper powder; and othermiscellaneous additives such as glass beads, glass spheres, talc,diatomaceous earth, alumina, silicate balloon, hydrated alumina, metaloxides and coloring agents.

The present invention also relates to a polyimide composite materialcomprising a polyamide made by the process of the invention and afibrous reinforcing material.

Fibrous reinforcing materials suitable for use with the polyimidecomposite material in this invention include, for example, glass fiberssuch as E-glass, S-glass, T-glass, C-glass and AR-glass; carbon fiberssuch as polyacrylonitrile base, pitch base and rayon base carbon fibers;aromatic polyamide fibers represented by Kevler (Trade mark of E.I. DuPont de Numeours & Co.); silicon carbide fibers such as Nicalon (Trademark of Nippon Carbon Co.); metallic fibers such as stainless steelfibers; alumina fibers and boron fibers. These fibers are used asunidirectional long fibers such as yarn, bundled unidirectional longfibers such as roving, tow and multidirectional continuous fibers suchas textiles, mats and felts.

These fibrous reinforcing materials are used singly or in combination.

These reinforcing materials should be selected to achieve the desiredproperties of the molded articles such as strength, elastic modulus,elongation at break, electrical properties and density. For example,carbon fibers or glass fibers are preferred when high values arerequired for specific strength and specific modulus of elasticity.Carbon fibers and metal fibers are preferred when shielding property forelectromagnetic field is required. Glass fibers are preferred whenelectrical insulation properties are required.

Fiber diameter and collected number of fibers depend upon the rawmaterials of fibers. For example, carbon fibers generally have a fiberdiameter of 4 to 8 μm and a collected number of 1,000 to 12,000. Finerdiameter of fibers is preferred due to favorable effect on themechanical properties of the molded articles obtained.

Surface treatment of the fibrous reinforcing materials is favorable forimproving affinity with the polyimide. For example, surface treatmentwith silane base or titanate base coupling agent is particularlypreferred for glass fibers.

Preferably, the fibrous reinforcing materials are present in thecomposite material in an amount of from about 5% to about 85%, morepreferably in an amount of from about 30% to about 70% by the volume ofthe composite material. When volume content of the fibrous a reinforcingmaterials is low, reinforcing effect cannot be expected. When the volumecontent is too high, the interlayer strength of molded articlesdecreases severely.

Any previously known method can be used for the preparation of thecomposite material from the polyimide and the fibrous reinforcingmaterial.

For example, the fused impregnation method may be employed wherein thefibrous reinforcing material is impregnated with the polyimide in amolten state. In the fluidized bed method, impregnation is carried outby using the polyimide powder in a state of floating in the air orsuspending in a liquid such as water. In the fluidized bed method, theimpregnated fibrous reinforcing material is dried, if necessary, andthen the polyimide in the fibrous reinforcing material is fused byheating. This process is particularly effective for providing theintegrated polyimide composite material. Finer particle size is desiredfor the polyimide powder at the impregnation. The preferred particlesize is less than the diameter of the fibrous monofilament.

In another method, the powder or a film of the polyimide is placed onone or both sides of the fibrous reinforcing material and pressed withheating. When the fibrous reinforcing material is a fabric, thepolyimide powder or film is alternately piled up with necessary sheetsof the fabric to form the desired thickness of the article to be moldedand is then pressed with heating. Thus impregnation and molding can beconducted at the same time and molded articles having a uniform resindispersion can be obtained.

Further methods for the fused impregnation have been representativelydescribed in Nakakura et al.; Japanese Laid-Open Patent 61-229534,61-229536 (1986) and Koba et al.; Japanese Patent Application 62-216253(1987) which corresponds to copending United States patent applicationSer. No. 189,955 filed on May 3, 1988. As an example of these method,the fibrous reinforcing material is impregnated by being contacted withthe molten resin on the surface of a hot roll or hot belt.

Specifically, a fiber sheet obtained by paralleling unidirectional longfibers such as tow which are drawn out of several bobbins or amultidirectional continuous fiber is applied a given tension in thedirection of take-up with a tension adjusting roll. The polyimide isfused by heating in an extruder. The fused polyimide is then extrudedthrough a die and applied to a lower belt on the surface of a hot rollmaintained at a prescribed temperature. Successively the above mentionedfiber sheet or multidirectional continuous fiber is impregnated bypassing through one or more hot rolls in a sandwiched condition betweenthe upper and lower pair of belts. The continuous impregnation method isparticularly preferred.

The composite material thus obtained is piled up and pressed withheating to obtain molded articles of desired shapes.

EXAMPLES

The present invention will be further clarified by the followingexamples which are intended to be purely exemplary of the invention.

EXAMPLE 1

To a reaction vessel equipped with a stirrer, reflux condenser andnitrogen inlet tube, 379 g (1.03 mole) of4,4'-bis(3-aminophenoxy)biphenyl and 5,371 g of N,N-dimethylacetamide asa solvent were charged. Then 217.8 g (1.00 mole) of pyromelliticdianhydride were added by portions at room temperature in a nitrogenatmosphere so as not to raise the temperature of the solution and werestirred for about 20 hours at the room temperature.

To the polyamic acid solution thus obtained 17.6 g (0.155 mole) ofglutaric anhydride were added at room temperature in a nitrogenatmosphere and further stirred for an hour. Then 202 g (2 moles) oftriethylamine and 306 g (3 moles) of acetic anhydride were addeddropwise to the solution. Yellow polyimide powder started to precipitateafter about one hour from the completion of dropwise addition. Thereaction mixture was further stirred for 10 hours at the roomtemperature. The resultant slurry was filtered, washed with methanol anddried at 180° C. for 2 hours. The polyimide powder obtained was 547 g.The polyimide powder had a glass transition temperature of 253° C., amelting point of 378° C. by DSC method and an inherent viscosity of 0.52dl/g. The inherent viscosity was measured at 35° C. in a solvent mixture(90/10 weight ratio of p-chlorophenol/phenol) at a concentration of 0.5g/100 ml solvent.

The relationship between the shear rate and the melt viscosity of thepolyimide powder thus obtained was measured by using a Japan PolymerSociety type flowtester (Trade mark, CFT-500; a product of ShimadzuSeisakusho Co.) with an orifice having a diameter of 0.1 cm and a lengthof 1 cm. After being maintained at 420° C. for 5 minutes, the meltviscosity was measured at various shear rates. The relationship betweenmelt viscosity and shear rate is illustrated by curve A in FIG. 1.

Comparative Example 1

The same procedures as described in Example 1 were carried out withoutusing glutaric anhydride. The polyimide powder obtained was 545 g andhad an inherent viscosity of 0.52 dl/g. By using the polyimide powder,the relationship between the melt viscosity and the shear rate wasmeasured with the flow tester as in Example 1. The results areillustrated by curve B in FIG. 1.

Curve B indicates a higher melt viscosity at lower shear rates (around10² l/sec ) than Curve A, which means difficulty of processing inComparative Example 1.

EXAMPLE 2

To a reaction vessel equipped with a stirrer, reflux condenser andnitrogen inlet tube, 368 g (1.0 mole) of4,4'-bis(3-aminophenoxy)biphenyl and 5,215 g of N,N-dimethylacetamide asa solvent were charged. Then 211.46 g (0.97 mole) of pyromelliticdianhydride was added by portions at room temperature in a nitrogenatmosphere so as not to raise the temperature of the solution andstirred for about 20 hours at room temperature.

To the polyamic acid solution thus obtained, 22.2 g (0.15 mole) ofphthalic anhydride were added at the room temperature in a nitrogenatmosphere and further stirred for one hour. Then 404 g (4 moles) oftriethylamine and 306 g (3 moles) of acetic anhydride were addeddropwise to the solution. Yellow polyimide powder started to precipitateafter about one hour from the completion of dropwise addition. Thereaction mixture was further stirred for 10 hours at the roomtemperature. The resultant slurry was filtered, washed with methanol anddried at 180° C. for 2 hours. The polyimide powder obtained was 536 g.The polyimide powder had a glass transition temperature of 256° C., amelting point of 378° C. and an inherent viscosity of 0.53 dl/g.

The melt viscosity of the polyimide powder thus obtained was repeatedlymeasured by using a Japan Polymer Society type flowtester. After holdingat 420° C. for 5 minutes, the sample was extruded with a pressure of 100kg/cm². The strand obtained was crushed and extruded again. Theprocedure was continuously repeated 5 times. The relationship betweenthe repeated number and the melt viscosity is illustrated by Curve A inFIG. 2. Almost no variation is found in the melt viscosity even thoughrepeated number is increased, which indicates good heat stability of themolten polyimide.

Comparative Example 2

The same procedures as described in Example 2 were carried out withoutphthalic anhydride. The polyimide powder obtained was 529 g and had aninherent viscosity of 0.52 dl/g.

The repeated measurement of the melt viscosity was carried out on thepolyimide powder thus obtained by the method described in Example 2. Theresults are illustrated by Curve B in FIG. 2. The melt viscosity wasincreased with the increase of repeated number. The heat stability ofthe molten polyimide thus obtained was inferior to that obtained inExample 2.

EXAMPLE 3

To a reaction vessel equipped with a stirrer, reflux condenser andnitrogen inlet tube, 412 g (1.03 mole) ofbis[4-(3-aminophenoxy)phenyl]sulfide and 5,747 g ofN,N-dimethylacetamide as a solvent were charged. Then 217 g (1.0 mole)of pyromellitic dianhydride and 9.53 g (0.062 mole) of1,2-cyclohexanedicarboxylic dianhydride were added at room temperaturein a nitrogen atmosphere so as not to raise the temperature of thesolution and stirred for 20 hours at room temperature. Then 202 g (2moles) of triethylamine and 306 g (3 moles) of acetic anhydride wereadded dropwise to the solution. The reaction mixture was stirred for 20hours at room temperature. The resultant light yellow slurry wasfiltered, washed with methanol and dried at 180° C. for 8 hours underreduced pressure. The light yellow polyimide powder thus obtained was597 g. The polyimide powder has a glass transition temperature of 232°C. and an inherent viscosity of 0.49 dl/g.

The melt viscosity of the polymide was measured at a cylindertemperature of 320° C., a residence time of 5 min and pressure of 100kg/cm². The melt viscosity was 5,600 poises. kg/cm².

The heat stability of the molten polyimide was evaluated by measuringthe variation of melt viscosity when the residence time of the moltenpolyimide was changed in the cylinder of the flow tester. The cylindertemperature was 320° C. The pressure at the measurement was 100kg/cm².The results are illustrated by Curve A in FIG. 3. Almost novariation was found in the melt viscosity even though the residence timewas extended, which indicates good heat stability of the moltenpolyimide.

Comparative Example 3

The same procedures as described in Example 3 were carried out without1,2-cyclohexanedicarboxylic anhydride.

The light yellow polyimide powder thus obtained had a glass transitiontemperature of 235° C. and an inherent viscosity of 0.49 dl/g. Thepolyimide had a melt viscosity of 8,000 poises at cylinder temperatureof 320° C., residence time of 5 minutes and under the pressure of 100kg/cm².

The heat stability of the molten polyimide was evaluated by measuringthe variation of melt viscosity when the residence time of the moltenpolyimide is changed in the cylinder of the flow tester. The meltviscosity was increased with the increase of residence time. The heatstability of the molten polyimide thus obtained was inferior to thatobtained in Example 3. The results are illustrated by Curve B in FIG. 3.

EXAMPLE 4

To a reaction vessel equipped with a stirrer, reflux condenser andnitrogen inlet tube, 400 g (1.0 mole) ofbis[4-(3-aminophenoxy)phenyl]sulfide and 5,580 g ofN,N-dimethylacetamide as a solvent were charged. Then 8.88 g (0.06 mole)of phthalic anhydride and 211 g (0.97 mole) of pyromellitic dianhydridewere added at room temperature in a nitrogen atmosphere so as not toraise the temperature of the solution and stirred for 20 hours at theroom temperature.

Then 404 g (4 moles) of triethylamine and 306 g (3 moles) of aceticanhydride were added dropwise to the solution. The reaction mixture wasstirred for 20 hours at room temperature. The resultant light yellowslurry was filtered, washed with methanol and dried at 180° C. for 8hours under reduced pressure. The light yellow polyimide powder thusobtained was 580 g. The polyimide powder had a glass transitiontemperature of 235° C. and an inherent viscosity of 0.49 dl/g.

The heat stability of the molten polyimide was evaluated by measuringthe variation of melt viscosity when the residence time of the moltenpolyimide was changed in the cylinder of the flow tester. The cylindertemperature was 320° C. The pressure at the measurement was 100 kg/cm².The results are illustrated by Curve A in FIG. 4. Almost no variationwas found in the melt viscosity even though the residence time wasextended, which indicates good heat stability of the molten polyimide.

Comparative Example 4

The same procedures as described in Example 4 were carried out withoutphthalic anhydride.

The light yellow polyimide powder thus obtained had a glass transitiontemperature of 235° C. and an inherent viscosity of 0.49 dl/g.

The heat stability of the molten polyimide was evaluated by measuringthe variation of melt viscosity when the residence time of the moltenpolyimide was changed in the cylinder of the flow tester. The meltviscosity was increased with the increase of residence time. The heatstability of the molten polyimide thus obtained was inferior to thatobtained in Example 4. The results are illustrated by Curve B in FIG. 4.

EXAMPLE 5

To a reaction vessel equipped with a stirrer, reflux condenser andnitrogen inlet tube, 400 g (1.03 moles) ofbis[4-(3-aminophenoxy)phenyl]ketone, 310 g (1.00 mole) ofbis(3,4-dicarboxyphenyl) ether dianhydride, 5.6 g (0.05 mole) ofcitraconic anhydride and 4,000 g of m-cresol were charged and graduallyheated with stirring in a nitrogen atmosphere. A brown transparenthomogeneous solution was obtained at about 120° C. The solution washeated to 150° C. Yellow polyimide powder was started to precipitateafter stirring for about 20 minutes at this temperature. After stirringthe reaction mixture for an additional 2 hours at 150° C. theprecipitate was filtered, washed with methanol and then acetone, anddried at 180° C. for 8 hours under reduced pressure. The polyimidepowder thus obtained was 676 g and had an inherent viscosity of 0.51dl/g, and a glass transition temperature of 200° C. The relationshipbetween the melt viscosity and the shear rate was measured at 280° C. bythe same procedures as described in Example 1. The results obtained areillustrated by Curve A in FIG. 5.

Comparative Example 5

The same procedures as described in Example 5 were carried out withoutcitraconic anhydride. The polyimide powder thus obtained had an inherentviscosity of 0.51 dl/g.

The relationship between the melt viscosity and the shear rate wasmeasured by the same conditions as in Example 5. The results obtainedare illustrated by Curve B in FIG. 5.

EXAMPLE 6

To a reaction vessel equipped with a stirrer, reflux condenser andnitrogen inlet tube, 396 g (1.0 mole) ofbis[4-(3-aminophenoxy)phenyl]ketone, 300.7 g (0.97 mole) ofbis(3,4-dicarboxyphenyl) ether dianhydride, 8.88 g (0.06 mole) ofphthalic anhydride and 4,000 g of m-cresol were charged and graduallyheated with stirring in a nitrogen atmosphere. A brown transparenthomogenous solution was obtained at about 120° C. The solution washeated to 150° C. A yellow polyimide powder started to precipitate afterstirring for about 20 minutes at 150° C. After stirring the reactionmixture for further 2 hours at the temperature, the precipitate wasfiltered, washed with methanol and then acetone, and dried at 180° C.for 8 hours under reduced pressure. The polyimide powder thus obtainedwas 662 g and had an inherent viscosity of 0.51 dl/g and a glasstransition temperature of 201° C.

The repeated extrusion test with the flow tester was carried out at 280°C. under a pressure of 100 kg/cm² by using the same conditions asdescribed in Example 2.

Almost no increase in the melt viscosity of the molten polyimide thusobtained was observed by the repeated extrusion. The results areillustrated in FIG. 6.

EXAMPLE 7

The polyimide powder was produced from 4,4'-bis(3-aminophenoxy)biphenyl,pyromellitic dianhydride and glutaric anhydride according to theprocedure of Example 1.

The composite material was manufactured from the polyimide thus obtainedand carbon fibers by the following method. FIG. 7 illustrates an outlineof the equipment used for the production.

Carbon fibers BESFIGHT HTA-7-3K (Trade mark of Toho Rayon Co.) are drawnfrom 100 bobbins (1), and 100 tows (2) are paralleled to one directionwith an aligner (3) and passed through tension adjusting rolls (4, 5, 6)to make a fiber sheet (7) having a width of 150 mm.

Separately, the polyimide powder fused by heating in an extruder (notindicated in FIG. 7) was extruded from a die (8) and applied to thesurface of a lower belt (10) with a thickness of 70 μm. The lower belt(10) was heated to 420° C. by three rolls (9) contacting with the lowerbelt (10), and the upper belt (12) was also heated to 420° C. by threerolls (11) contacting with the upper belt (12). Then the above obtainedfiber sheet was sandwiched between the upper and lower belts, and passedthrough three impregnation rolls (13) at a rate of 20 cm/min undertension of 150 kg. The impregnation rolls (13) had a diameter of 240 mmand were heated to 350° C. The polyimide impregnated carbon fibercomposite material (14) thus obtained was cooled, passed through take-uprolls (15, 16, 17) and wound up by the winding shaft (18).

The composite material thus obtained had a width of 150 mm and thicknessof 0.13 mm.

Then 20 sheets of the above polyimide composite material wereunidirectionally piled up and hot pressed at 400° C. for 20 minutesunder pressure of 30 kg/cm² to obtain a plate having dimensions of200×200×2.5 (thickness) mm. Volume percentage of the fibrous reinforcingmaterial (hereinafter abbreviated as Vf), void ratio, flexural strengthand flexural modulus were measured on the plate thus obtained. The platehad a Vf of 60%, void ratio of 1% or less, flexural strength of 191kg/mm² and flexural modulus of 12,300 kg/mm². These results indicatedgood properties of the plate. Vf and void ratio were calculated from thedensity and weight percentage of the fibrous reinforcing material of theplate. Flexural strength and flexural modulus were measured inaccordance with JIS K 7230.

EXAMPLE 8

The polyimide powder was produced from 4,4'-bis(3-aminophenoxy)biphenyl,pyromellitic dianhydride and phthalic anhydride according to theprocedure of Example 2.

The same procedures as described in Example 7 were carried out for themanufacture of the composite material from the polyimide powder thusobtained and carbon fiber.

The operation for the manufacture of the composite material wascontinued for 5 hours. No change was observed during the operation onthe flowability of molten polyimide. The resultant composite materialcould be smoothly wound up without fiber breakage. The compositematerial thus obtained had a width of 150 mm and a thickness of 0.13 mm.

Then 20 sheets of the above obtained polyimide composite material wereunidirectionally piled up and hot pressed at 400° C. for 20 minutesunder pressure of 50 kg/cm² to obtain a plate having dimensions of200×200×2.5 (thickness) mm. The plate obtained had a Vf of 60%, voidratio of 1% or less, flexural strength of 195 kg/mm² and flexuralmodulus of 12,500 kg/mm². These results indicated good properties of theplate.

Comparative Example 6

The polyimide powder was produced from 4,4'-bis(3-aminophenoxy)biphenyland pyromellitic dianhydride according to the procedure of ComparativeExample 2.

The same procedures for the production of the composite material asdescribed in Example 7 were carried out by using the polyimide powderthus obtained. After 30 minutes from the start of the operation, moltenpolyimide caused gelation and release of fibers from the upper and lowerbelts became difficult. Finally the operation was stopped. A part of thecomposite material formed in this operation was molded by the sameprocedures as described in Example 8 and its physical properties wasevaluated. The molded plate had a Vf of 60%, void ratio of 6.5%,flexural strength of 98 kg/mm² and flexural modulus of 6,500 kg/mm². Theextremely low strength and modulus resulted from a significant decreasein flowability and insufficient defoaming.

EXAMPLES 9-12

The polyimide composite materials were obtained by carrying out the sameprocedures as described in Example 7 except that the kinds of fibrousreinforcing materials and the applied thickness of the molten polyimideto the belt were changed as illustrated in Table 1. Thus a polyimidecomposite material was obtained. Several composite materials asillustrated in Table 1 were piled up and processed by the sameprocedures as described in Example 7. The properties of the plateobtained were shown in Table 1.

EXAMPLES 13-14

The same procedures as described in Example 7 were carried out exceptthat the kinds of fibrous reinforcing materials and the appliedthickness of the molten polyimide to the belt were changed asillustrated in Table 1, and the tension was changed to 30 kg. ThusPolyimide composite materials were obtained. Several composite materialas illustrated in Table 1 were piled up and processed by the sameprocedures as described in FIG. 7. The properties of the plate thusobtained are illustrated in Table 1.

EXAMPLES 15-18

The same procedures as in Example 8 were carried out except that thekinds of fibrous reinforcing materials and the applied thickness of themolten polyimide to the belt were changed as illustrated in Table 1.Thus polyimide composite materials were obtained. Several of compositematerials as illustrated in Table 1 were piled up and processed by thesame procedures as in Example 8. Properties of the plate thus obtainedare illustrated in Table 1.

EXAMPLES 19-20

The same procedures as Example 8 were carried out except that the kindsof fibrous reinforcing materials and the applied thickness of the moltenpolyimide to the belt were changed as illustrated in Table 1, and thetension was changed to 30 kg. Thus polyimide composite materials wereobtained. Several of the composite material as illustrated in Table 1were piled up and processed by the same procedures as Example 8.Properties of the plate thus obtained are illustrated in Table 1.

EXAMPLE 21

An aluminium frame having inside dimensions of 30 cm x 30 cm and athickness of 1.0 mm was placed on a heat resistant release film of 50 μmthick, and 5 g of the polyimide powder obtained in Example 1 wasuniformly dispersed within the frame. Then the frame was removed, and acarbon fiber fabric BESFIGHT W-3101 (Trade mark of Toho Rayon Co.) wasplaced on the polyimide powder dispersed above. Another 5 g of thepolyimide powder was uniformly dispersed on the above fabric. Acommercial heat resistant release film was put on the dispersedpolyimide powder and pressed in a metal mold at 400° C. for 10 minuteswith the pressure of 70 kg/cm².After cooling to 250° C. with the samepressure, the molded product was taken out of the mold and the releasefilms were removed.

The composite material thus obtained was divided into 6 portions, piledup and processed by the same procedures as described in Example 1. Theresultant plate had a Vf of 60%, flexural strength of 82 kg/mm² andflexural modulus of 6,300 kg/mm².

                                      TABLE 1                                     __________________________________________________________________________    Fibrous reinforcing material                                                                           Volume                                                                             Number                                                                             Flexural                                                                            Flexural                                  Applied             content                                                                            of piled                                                                           strength                                                                            modulus                              Example                                                                            thickness                                                                          Material                                                                              Form   (%)  sheet                                                                              (kg/mm.sup.2)                                                                       (kg/mm.sup.2)                        __________________________________________________________________________     9   200  Carbon fiber                                                                          Tow    30   12   93    6,200                                10    40  Carbon fiber                                                                          Tow    70   26   215   13,500                               11   105  Glass fiber                                                                           Roving 60   12   141   5,000                                12    80  Aromatic                                                                              Roving 60   12   70    5,700                                          polyamide fiber                                                     13   100  Carbon fiber                                                                          Plain woven                                                                          60   16   85    6,500                                                  fabric                                                      14    70  Glass fiber                                                                           Plain woven                                                                          60   22   67    2,300                                                  fabric                                                      15   200  Carbon fiber                                                                          Tow    30   12   96    6,300                                16    40  Carbon fiber                                                                          Tow    70   26   217   13,600                               17   105  Glass fiber                                                                           Roving 60   12   142   5,100                                18    80  Aromatic                                                                              Roving 60   12   71    6,000                                          polyamide fiber                                                     19   100  Carbon fiber                                                                          Plain woven                                                                          60   16   85    6,800                                                  fabric                                                      20    70  Glass fiber                                                                           Plain woven                                                                          60   22   68    2,400                                                  fabric                                                      __________________________________________________________________________

EXAMPLE 22

The same procedures as described in Example 21 were carried out exceptthat the polyimide powder obtained in Example 2 was used in place of thepolyimide powder obtained in Example 1.

The plate thus obtained had a Vf of 60%, flexural strength of 83 kg/mm²and flexural modulus of 6,500 kg/mm².

EXAMPLE 23

In Example 2, 315 g (0.98 mole) of 3,3',4,4'-benzophenonetetracarboxylicdianhydride was used in place of 211.46 g of pyromellitic dianhydride.The polyimide powder was 617 g and had an inherent viscosity of 0.53dl/g.

The polyimide powder produced according to the procedure above wassubjected to impregnation process by the same procedures as described inExample 7 except that impregnation temperature was changed to 400° C.The operation was smoothly continued for 5 hours. No change was observedon the flowability of the molten polyimide resin during the operation.

The polyimide composite material thus obtained was hot pressed by thesame procedures as Example 7 except that the temperature was changed to380° C. The plate obtained had a flexural strength of 190 kg/mm² and aflexural modulus of 12,100 kg/mm².

Comparative Example 7

The same procedures as Example 23 were carried out without phthalicanhydride. The polyimide powder thus obtained had an inherent viscosityof 0.53 dl/g.

The same procedures for the production of the composite material asdescribed in Example 7 were carried out by using the polyimide powderthus obtained. After about 20 minutes from the start of the operation,molten polyimide caused gelation and release of fibers from the upperand lower belts became difficult. Finally the operation was stopped. Apart of the composite material formed in the operation was molded by thesame procedures as Example 8 and the physical properties were evaluated.The molded plate had a Vf of 59%, void ratio of 6.8%, flexural strengthof 95 kg/mm² and flexural modulus of 5,800 kg/mm². The extremely lowstrength and modulus were resulted from significant decrease inflowability and insufficient defoaming of the molten polyimide.

EXAMPLE 24

The polyimide powder was produced from bis[4-(3-aminophenoxy)phenyl]sulfide, pyromellitic dianhydride and 1,2-cyclohexanedicarboxylicanhydride according to the procedure of Example 3.

The polyimide powder was subjected to impregnation process by the sameprocedures as described in Example 7 except that impregnationtemperature was changed to 340° C. Then the resultant composite materialwas hot pressed by the same procedures as Example 7 except that thetemperature was changed to 320° C. The plate thus obtained had aflexural strength of 180 kg/mm² and flexural modulus of 11,100 kg/mm².

EXAMPLE 25

The polyimide powder was produced from bis[4-(3-aminophenoxy)phenyl]sulfide, pyromellitic dianhdyride and phthalic anhydride according tothe procedure of Example 4.

The polyimide powder thus obtained was subjected to impregnation processby the same procedures as described in Example 7 except thatimpregnation temperature was changed to 340° C. The implegnatingoperation was smoothly continued for 5 hours. No change was observed onthe flowability of the molten polyimide during the operation.

The composite material thus obtained was then hot pressed by the sameprocedures as described in Example 8 except that the temperature waschanged to 320° C. The plate thus obtained had a flexural strength of182 kg/mm² and a flexural modulus of 11,300 kg/mm².

Comparative Example 8

The polyimide powder was produced from bis[4-(3-aminophenoxy)phenyl]sulfide and pyromellitic dianhydride according to the procedure ofComparative Example 4.

The same procedures for the production of the composite material asdescribed in Example 7 were carried out by using the polyimide powderthus obtained. After about 35 minutes from the start of operation,molten polyimide caused gelation and release of fibers from the upperand lower belts became difficult. Finally the operation was stopped.

A part of the composite material formed in the operation was molded bythe same procedures as Example 8 and evaluated physical properties. Themolded plate had a Vf of 60%, void ratio of 4.9%, flexural strength of98 kg/ma2 and flexural modulus of 6,700 kg/mm². The extremely lowstrength and modulus were resulted from significant decrease inflowability and insufficient defoaming of the molten polyimide.

EXAMPLE 26

The polyimide powder was produced from bis[4-(3-aminophenoxy)phenyl]ketone, bis(3,4-dicarboxyphenyl) ether dianhydride and citraconicanhydride according to the procedure of Example 5.

The polyimide powder thus obtained was subjected to impregnation processby the same procedures as described in Example 7 except thatimpregnation temperature was changed to 320° C.

The composite material thus obtained was then hot pressed by the sameprocedures as described in Example 7 except that the temperature waschanged to 300° C. The plate thus obtained had a flexural strength of173 kg/mm² and a flexural modulus of 10,300 kg/mm².

EXAMPLE 27

The polyimide powder was produced from bis[4-(3-aminophenoxy)phenyl]ketone, bis(3,4-dicarboxyphenyl) ether dianhydride and phthalicanhydride according to the procedure of Example 6.

The polyimide powder thus obtained was subjected to impregnation processby the same procedures as described in Example 7 except thatimpregnation temperature was changed to 320° C. The impregnationoperation was smoothly continued for 5 hours. No change was observed onthe flowability of the molten polyimide during the operation.

The composite material thus obtained was then hot pressed by the sameprocedures as described in Example 8 except that the temperature waschanged to 300° C. The plate thus obtained had a flexural strength of179 kg/mm² and a flexural modulus of 10,900 kg/m².

What is claimed is:
 1. A process for preparing a polyimide comprisingreacting(a) at least one aromatic diamine represented by the formula (I)##STR7## wherein X represents a direct bond or a radical selected fromthe group consisting of a C₁ -C₁₀ divalent hydrocarbon radical, ahexafluorinated isopropylidene radical, a carbonyl radical, a thioradical and a sulfonyl radical; and Y₁ a process for preparing apolyimide comprising reacting (a) at least one aromatic diaminerepresented by the formula (I) ##STR8## wherein X represents a directbond or a radical selected from the group consisting of a C₁ -C₁₀divalent hydrocarbon radical, a hexafluorinated isopropylidene radical,a carbonyl radical, a thio radical and a sulfonyl radical; and Y₁, Y₂,Y₃ and Y₄ may be the same or different and represent a radical selectedfrom the group consisting of a hydrogen atom, a lower alkyl radical, alower alkoxy radical, a chlorine atom and a bromine atom; (b) at leastone tetracarboxylic dianhydride represented by the formula (II) ##STR9##wherein R represents a tetravalent radical selected from the groupconsisting of an aliphatic radical having at least two carbon atoms, acyclic aliphatic radical, a monocyclic aromatic radical, a fusedpolycyclic aromatic radical, a polycyclic aromatic radical wherein thearomatic rings are linked together directly or by a bridged member; and(c) at least one dicarboxylic anhydride represented by the formula (III)##STR10## wherein Z represents a divalent radical selected from thegroup consisting of an aliphatic radical, a cyclic aliphatic radical, amonocyclic aromatic radical, a fused polycyclic aromatic radical and apolycyclic aromatic radical wherein the aromatic rings are linkedtogether directed or via a bridged member; to form a polyamic acid; anddehydrating or imidizing said polyamic acid to form a polyimide.
 2. Theprocess of claim 1 wherein the molar ratio of said tetracarboxylicdianhydride to said aromatic diamine is from about 0.9 to about 1.0 moleof tetracarboxylic dianhydride per mole of aromatic diamine.
 3. Theprocess of claim 1 wherein the molar ratio of said dicarboxylicanhydride to said aromatic diamine is from about 0.001 to about 1.0 moleof dicarboxylic anhydride per mole of aromatic diamine.
 4. The processof claim 3 wherein said molar ratio is from about 0.01 to about 0.5 moleof dicarboxylic anhydride per mole of aromatic diamine.
 5. The processof claim 2 wherein the molar ratio of said dicarboxylic anhydride tosaid aromatic diamine is from about 0.001 to about 1.0 mole ofdicarboxylic anhydride per mole of aromatic diamine.
 6. The process ofclaim 1 wherein said aromatic diamine is selected from the groupconsisting of 4,4'-bis(3-aminophenoxy)biphenyl,2,2-bis[4-(3-aminophenoxy)phenyl]propane,bis[4-(3-aminophenyoxy)phenyl]ketone,bis[4-(3-aminophenoxy)phenyl]sulfide andbis[4-(3-aminophenoxy)phenyl]-sufone.
 7. The process of claim 1 whereinsaid tetracarboxylic dianhydride is selected from the group consistingof pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylicdianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride,bis(3,4-dicarboxyphenyl)ether dianhydride and4,4'-(p-phenylenedioxy)diphthalic dianhydride.
 8. The process of claim 1wherein said dicarboxylic anhydride is selected from the groupconsisting of glutaric anhydride, citraconic anhydride, tetraconicanhydride, 1,2-cyclobutanedicarboxylic anhydride, 1,2-hexanedicarboxylicanhydride, pthalic anhydride, 3,4-benzophenonedicarboxylic anhydride,3,4-dicarboxyphenyl phenyl ether anhydride, 3,4-biphenyldicarboxylicanhydride, 3,4-dicarboxyphenyl phenyl sulfide anhydride and3,4-dicarboxyphenyl phenyl sulfone.
 9. The process of claim 1 whereinthe reaction temperature is from about 0° C. to about 250° C.
 10. Theprocess of claim 9 wherein the reaction temperature is no greater thanabout 60° C.
 11. The process of claim 1 wherein the reaction time isfrom about 4 hours to about 24 hours.
 12. The process of claim 1 whereinsaid polyamic acid is dehydrated by heating at a temperature of fromabout 100° C. to about 400° C.
 13. A process for preparing a polyimidecomprising reacting in an organic solvent at a temperature of from about60° C. to about 250° C.(a) at least one aromatic diamine represented bythe formula (I) ##STR11## wherein X represents a direct bond or aradical selected from the group consisting of a C₁ -C₁₀ divalenthydrocarbon radical, a hexafluorinated isopropylidene radical, acarbonyl radical, a thio radical and a sulfonyl radical; and Y₁, Y₂, Y₃and Y₄ may be the same or different and represent a radical selectedfrom the group consisting of a hydrogen atom, a lower alkyl radical, alower alkoxy radical, a chlorine atom and a bromine atom; (b) at leastone tetracarboxylic dianhydride represented by the formula (II)##STR12## wherein R represents a tetravalent radical selected from thegroup consisting of an aliphatic radical having at least two carbonatoms, a cyclic aliphatic radical, a monocyclic aromatic radical, afused polycyclic aromatic radical, a polycyclic aromatic radical whereinthe aromatic rings are linked together directly or by a bridged member;and (c) at least one dicarboxylic anhydride represented by the formula(III) ##STR13## wherein Z represents a divalent radical selected fromthe group consisting of an aliphatic radical, a cyclic aliphaticradical, a monocyclic aromatic radical, a fused polycyclic aromaticradical and a polycyclic aromatic radical wherein the aromatic rings arelinked together directed or via a bridged member; to form a polyimide.14. The process of claim 13 wherein the molar ratio of saidtetracarboxylic dianhydride to said aromatic diamine is from about 0.9to about 1.0 mole of tetracarboxylic dianhydride per mole of aromaticdiamine.
 15. The process of claim 13 wherein the molar ratio of saiddicarboxylic anhydride to said aromatic diamine is from about 0.001 toabout 1.0 mole of dicarboxylic anhydride per mole of aromatic diamine.16. The process of claim 15 wherein said molar ratio is from about 0.01to about 0.5 mole of dicarboxylic anhydride per mole of aromaticdiamine.
 17. The process of claim 14 wherein the molar ratio of saiddicarboxylic anhydride to said aromatic diamine is from about 0.001 toabout 1.0 mole of dicarboxylic dianhydride per mole of aromatic diamine.18. The process of claim 13 wherein said aromatic diamine is selectedfrom the group consisting of 4,4'-bis(3-aminophenoxy)biphenyl,2,2-bis[4-(3-aminophenoxy)phenyl]propane,bis[4-(3-aminophenoxy)phenyl]ketone,bis[4-(3-aminophenoxy)phenyl]sulfide andbis[4-(3-aminophenoxy)phenyl]-sulfone.
 19. The process of claim 13wherein said tetracarboxylic dihydride is selected from the groupconsisting of pyromellitic dianhydride,3,3'4,4'-benzophenoetetracarboxylic dianhydride,3,3',4,4'-biphenyltetracarboxylic dianhydride,bis(3,4-dicarboxyphenyl)ether dianhdyride and4,4'-(p-phenylenedioxy)diphthalic dianhydride.
 20. The process of claim3 wherein said dicarboxylic anhydride is selected from the groupconsisting of glutaric anhydride, citraconic anhydride, tetraconicanhydride, 1,2-cyclobutanedicarboxylic anhydride, 1,2-hexanedicarboxylicanhydride, pthalic anhydride, 3,4benzophenonedicarboxylic anhydride,3,4-dicarboxyphenyl phenyl ether anhydride, 3,4-biphenyldicarboxylicanhydride, 3,4dicarboxyphenyl phenyl sulfide anhydride and3,4dicarboxyphenyl phenyl sulfone.
 21. A polyimide composition preparedby the process of claim 1 comprising recurring units represented by theformula ##STR14## wherein X represents a direct bond or a radicalselected from the group consisting of a C₁ -C₁₀ divalent hydrocarbonradical, a hexafluorinated isopropylidene radical, a carbonyl radical, athio radical and a sulfonyl radical; Y₁, Y₂, Y₃ and Y₄ may be the sameor different and represent a radical selected from the group consistingof a hydrogen atom, a lower alkyl radical, a lower alkoxy radical, achlorine atom and a bromine atom; and R represents a teteravalentradical selected from the group consisting of an aliphatic radical andhaving 2 or more carbon atoms, a cyclic aliphatic radical, a monocyclicaromatic radical wherein the aromatic rings are linked together directlyor by a bridged member.
 22. A polyimide composition prepared by theprocess of claim 1 comprising recurring units represented by the formula##STR15## wherein X represents a direct bond or a radical selected fromthe group consisting of a C₁ -C₁₀ divalent hydrocarbon radical, ahexafluorinated isopropylidene radical, a carbonyl radical, a thioradical and a sulfonyl radical; Y₁, Y₂, Y₃ and Y₄ may be the same ordifferent and represent a radical selected from the group consisting ofa hydrogen atom, a lower alkyl radical, a lower alkoxy radical, achlorine atom and a bromine atom; and R represents a teteravalentradical selected from the group consisting of an aliphatic radical andhaving 2 or more carbon atoms, a cyclic aliphatic radical, a monocyclicaromatic radical wherein the aromatic rings are linked together directlyor by a bridged member.
 23. A polyimide composite material comprisingfrom about 15% to about 95% of the polyimide of claim 1 and from about5% to about 85% of at least one fibrous reinforcing material.
 24. Thepolyimide composite material of claim 23 wherein said fibrousreinforcing material is selected from the group consisting of glassfiber, carbon fiber, aromatic polyimide fiber, metal fiber, aluminafiber and boron fiber.
 25. A polyimide composite material comprisingfrom about 15% to about 95% of the polyimide of claim 13 and from about5% to about 85% of at least one fibrous reinforcing material.
 26. Thepolyimide composite material of claim 25 wherein said fibrousreinforcing material is selected from the group consisting of glassfiber, carbon fiber, aromatic polyimide fiber, metal fiber, aluminafiber and boron fiber.
 27. A process for preparing a polyimidecomprising reacting(a) at least one aromatic diamine represented by theformula (I) ##STR16## wherein X represents a direct bond or a radicalselected from the group consisting of a C₁ -C₁₀ divalent hydrocarbonradical, a hexafluorinated isopropylidene radical, a carbonyl radical, athio radical and a sulfonyl radical; and Y₁, Y₂, Y₃ and Y₄ may be thesame or different and represent a radical selected from the groupconsisting of a hydrogen atom, a lower alkyl radical, a lower alkoxyradical, a chlorine atom and a bromine atom; (b) at least onetetracarboxylic dianhydride represented by the formula (II) ##STR17##wherein R represents a tetravalent radical selected from the groupconsisting of an aliphatic radical having at least two carbon atoms, acyclic aliphatic radical, a monocyclic aromatic radical, a fusedpolycyclic aromatic radical, a polycyclic aromatic radical wherein thearomatic rings are linked together directly or by a bridged member; and(c) at least one dicarboxylic anhydride represented by the formula (III)##STR18## wherein Z represents a divalent radical selected from thegroup consisting of an aliphatic radical, a cyclic aliphatic radical, amonocyclic aromatic radical, a fused polycyclic aromatic radical and apolycyclic aromatic radical wherein the aromatic rings are linkedtogether directed or via a bridged member.
 28. The process of claim 27wherein the molar ratio of said tetracarboxylic dianhydride to saidaromatic diamine is from about 0.9 to about 1.0 mole of tetracarboxylicdianhydride per mole of aromatic diamine.
 29. The process of claim 27wherein the molar ratio of said dicarboxylic anhydride to said aromaticdiamine is from about 0.001 to about 1.0 mole of dicarboxylic anhydrideper mole of aromatic diamine.
 30. The process of claim 29 wherein saidmolar ratio is from about 0.01 to about 0.5 mole of dicarboxylicanhydride per mole of aromatic diamine.
 31. The process of claim 28wherein the molar ratio of said dicarboxylic anhydride to said aromaticdiamine is from about 0.001 to about 1.0 mole of dicarboxylic anhydrideper mole of aromatic diamine.
 32. The process of claim 27 wherein saidaromatic diamine is selected from the group consisting of4,4'-bis(3-aminophenoxy)biphenyl,2,2-bis[4-(3-aminophenoxy)phenyl]propane,bis[4-(3-aminophenoxy)phenyl]ketone,bis[4-(3-aminophenoxy)-phenyl]sulfide andbis[4-(3-aminophenoxy)phenyl]-sulfone.
 33. The process of claim 27wherein said tetracarboxylic dianhydride is selected from the groupconsisting of pyromellitic dianhydride,3,3',4,4'-benxophenonetetracarboxylic dianhydride,3,3',4,4'-biphenyltetracarboxylic dianhydride,bis(3,4-dicarboxyphenyl)ether dianhydride and4,4'-(p-phenylenedioxy)diphthalic dianhydride.
 34. The process of claim27 wherein said dicarboxylic anhydride is selected from the groupconsisting of glutaric anhydride, citraconic anhydride, tetraconicanhydride, 1,2-cyclobutanedicarboxylic anhydride, 1,2-hexanedicarboxylicanhydride, phthalic anhydride, 3,4-benzophenononedicarboxylic anhydride,3,4-dicarboxyphenyl phenyl ether anhydride, 3,4-biphenyldicarboxylicanhydride, 3,4-dicarboxyphenyl phenyl sulfide anhydride and3,4-dicarboxyphenyl phenyl sulfone.
 35. The process of claim 27 whereinthe reaction temperature is from about 0° C. to about 250° C.
 36. Theprocess of claim 35 wherein the reaction temperature is no greater thanabout 60° C.
 37. The process of claim 27 wherein the reaction time isfrom about 4 hours to about 24 hours.